Work layer "Mask"

[#1]

The essence of the problem is as follows. There is a layer mode "mask" while working on the timeline it behaves appropriately (at the bottom of the screenshots), but when exporting to SWF half way stops working (green normal, red is where it stopped ("shadow" on the right screen disappears)). Any ideas? Animate CC2019

[#2]

Have you tried moving the red section to a different layer?

Only put the stuff you want to be masked on the masked layer.